This section is from "The American Cyclopaedia", by George Ripley And Charles A. Dana. Also available from Amazon: The New American Cyclopędia. 16 volumes complete..
Anodyne (Gr. av privative and pain), a term properly applied, not to medicines which relieve pain by removing its cause, but to those which merely diminish the conducting power of the nerves of sensation, or which render the brain less susceptible to or less conscious of pain. The principal medicines of this kind are opium, belladonna, and hyoscyamus, with their alkaloids, Indian hemp, ether, and chloroform. The last two are usually called anaesthetics, because they diminish the power of the brain to receive impressions from any external source. The use of anodynes is generally to be looked upon as the substitution of a lesser evil for a greater, and a habitual resort to them is always, if possible, to be avoided.